The fourth round of peace talks between the Sri Lankan government and Tamil rebels are expected to be the toughest yet. Thorny security issues threaten to bog down this round of peace talks, but negotiators remain optimistic they will continue to produce results.

The core of the controversy is the government's demand that the Tamil Tiger rebels disarm before it closes military camps in Sri Lanka's war-torn north. The camps must be closed so refugees can return to their homes in high-security zones.

The chief Tamil negotiator, Anton Balasingham, says the security issues must be resolved before the talks can move forward. He warns that the rebels will not disarm. He and the government's top negotiator, GL Peiris, held informal, closed-door talks Sunday.

The Norwegian-sponsored talks, which began last September, already have made progress. Most significantly, the Tamils have dropped their demand for an independent state and instead agreed to autonomy under a federal state.

The negotiations are aimed at ending the 19-year civil war that has claimed more than 60,000 lives and devastated the country's economy. The ethnic Tamil minority says it has long been discriminated against by Sri Lanka's Sinhalese majority.

Sanjay Gathia, from the human rights group Asia Forum, said "the negotiations will be definitely quite tough. But it won't derail the talks as such, because I think both the parties have come so far and tried to resolve certain issues quite open-heartedly."

Mr. Gathia said any agreement on security issues will likely include concessions from both sides. "Peiris is expecting some kind of response measure from the LTT, in case the government is trying to take some action, you know, for like probably reducing the number of army personnel in those areas," he said.

Negotiators have said the peace talks hold the best hope for ending the civil war.